Coolants are often needed in stationary and vehicular engines, for example internal combustion engines, to maintain system temperatures suitable for effective operation. Such coolants, for example, liquid coolants, are circulated through an engine cooling or coolant system and frequently require filtering and/or additive addition to maintain effective system operation. Filtering of a circulating coolant removes debris and particulate matter from the coolant. Long term use of a coolant often requires that the coolant be fortified with one or more supplemental additives, such as corrosion inhibitors, anti-foaming agents and/or other known coolant additives for maintaining quality of the coolant and/or cooling system. Such additives are typically directly added to the coolant in the form of a concentrated aqueous solution, or in solid granular or powder form.
Traditionally, additives such as anti-foulants, anti-scaling agents, corrosion inhibitors, buffering and pH agents, microbiocides and the like are added directly to aqueous or glycol-based liquid coolants of cooling systems on an “as-needed” basis, or at regularly scheduled time periods. Coolant additives provide at least one benefit to the coolant and/or cooling system, for example, to prevent scale deposition, corrosion of metal surfaces and similar fouling of the cooling system, maintain proper acidity/alkalinity, e.g., pH levels in the coolant and the like benefit. As used herein, a cooling system includes, without limitation, an open circulating cooling system, for example, a cooling tower and the like; and a substantially closed cooling system, for example, an internal combustion engine cooling system, such as those associated with vehicles, heavy equipment and the like. Also, as used herein, a “system” preferably includes a circulating coolant, for example, coolant liquid. In addition, a system may include a circulating liquid pump, tubing, etc.
In many cooling systems, it is preferable to maintain a steady level of additives. For example, the presence of microbiocides is especially important in an aqueous system such as cooling systems employed in cooling towers. Cooling towers are often run continuously or are at least available for use for considerable lengths of time. Typically, such cooling systems do not have sufficient aeration and exposure to sunlight to prevent microbial, especially bacterial and fungal, growth. In particular, many cooling systems use fill composed of beads of synthetic polymer or other materials, in order to extend the amount of heat exchange surface area. This type of construction greatly aggravates the problem of microbiological growth, since it provides an ideal physical environment for the propagation of troublesome microbes. If left untreated, such microorganisms may flourish and produce colonies extensive enough to give rise to problems of biofilm blockage of heat exchange surfaces, as well as clogging of the components of the water transporting apparatus used in operating the aqueous system. It would clearly be advantageous to maintain an effective level of additives, such as microbiocides, in the coolants used in such cooling systems.
Various methods of introducing additives to a cooling system have been developed with an object of maintaining an appropriate, effective level of additives in the system. For instance, a solid additive material in the form of powders, pellets and the like, may be added directly to the cooling system, to be dissolved into the circulating coolant. However, this method is not effective in maintaining a steady concentration level of additive within the system. Initially, there would be a high level of the additives released into the system, and within a short time the additives are depleted. Additionally, a significant drawback of this method is the danger of overdosing the system with particular additives when the additives are initially dissolved. The overdosing is dangerous in that it can result in system erosion and corrosion problems.
Attempts have been made in the prior art to address particular water treatment systems by using controlled release coatings. For example, Characklis in U.S. Pat. No. 4,561,981 disclosed a method for controlling, preventing or removing fouling deposits, particularly in pipelines, storage tanks and the like by microencapsulating fouling control chemicals in a slow release coating. The coating material is described as being any material compatible with the fouling control chemical which is capable of sticking to the fouling deposit site.
Recently, Mitchell et al. in U.S. Pat. No. 6,010,639 disclosed that a terpolymer may be used as a coating for cooling additives.
Despite the efforts of the prior art, a need still exists for a coolant additive composition for providing a slow, sustained release of additive into a coolant in a cooling system.